Stirrers or mixers



May 11, 1965 A. IVANOFF STIRRERS OR MIXERS Filed NOV. 3. 1961 FIG.8

FIG. IO

INVENTOR ALEXANDER IVAN F ATTORN Y United States Patent 3,182,970 STRS0R MIXERS Alexander Ivanoit, Greenwich, Conn, assignor to Hayward Tyler& Company Limited Filed Nov. 3, 1961, Ser. No. 150,046 10 Claims. (Cl.259-95) This invention relates to liquid mixing devices of the kindcomprising an oscillating impeller having vanes which extend along theaxis of oscillation and project outwardly from it.

The normal construction of impeller used in devices of this kind merelypushes to and fro the liquid in the vicinity of the impeller, with theresult that liquid more distant from the impeller is not thoroughly oruniformly mixed.

The present invention provides a device of the kind above mentionedwhich is operable to produce a unidirectional continuous flow of liquidthrough the impeller, resulting in efficient and uniform mixing of theliquid.

It is an object of the invention to provide a liquid mixing device ofthe kind above referred to in which means are provided for amplifyingthe rotary oscillations applied to the shaft so that the impeller has anincreased amplitude of oscillation.

To attain the purpose, the shaft which carries the impeller is flexiblein torsion and it is oscillated at a frequency substantially equal tothe resonance frequency of oscillation of the system comprising theimpeller, the shaft and liquid lying between the vanes of the impeller.

Further features of the invention are based on the discovery that threefactors exert an influence on the estab lishment of continuous flow,namely the amplitude of oscillation, the number of vanes and the ratioof the axial length of the vanes to the diameter of the impeller, andthat an increase in any one of these factors favors the establishment ofcontinuous flow.

It is, however, undesirable to oscillate the impeller through a largeangle because of the excessive vibration which is caused and of theincreased danger of seals collapsing.

In accordance, therefore, with a further feature of the presentinvention, in a device of the kind referred to, having an impeller whichis open ended, that is an impeller in which fluid can flow at both endsof the impeller through the gaps between the radial edges of adjacentvanes, the ratio of the axial length of the vanes to the diameter of theimpeller is not less than 2/5 and the product of this ratio and thenumber of vanes is not less than with an impeller so constructed, it isfound that continuous flow can be established by oscillating theimpeller through a minimum angle of 5".

If the impeller is closed at one end by a shroud which fills the gapsbetween the radial edges of adjacent vanes, the van s behave as halfvanes of double length and in consequence, for continuous flow to beestablished with a minimum amplitude of oscillation of 5, the minimumvalue of the said product is 2.5.

By maintaining the ratio of the axial length of the vanes to thediameter of the impeller at a minimum value of 2/5, the required numberof vanes is kept small. Preferably the value of the said ratio isapproximately 1:1.

Thus, for example, in an open ended impeller having six vanes the lengthof each vane being equal to the impeller diameter, the value of the saidproduct is 6 1=6. Again, if there are twelve vanes, the length of eachbeing 42% of the impeller diameter, the value of the product is 12.42=5.04.

For an impeller having an end shroud, with siX vanes equal in length tohalf the impeller diameter, the value of the product is 6 .5=3.

See

Some preferred constructions in accordance with the invention aredescribed below, by way of example, with reference to the accompanyingdrawings, in which:

FIGURE 1 is a part sectional elevation of a mixing pump in accordancewith the invention;

FIGURE 2 is a view on the line BB of FIGURE 1;

FIGURE 3 is a view on the line AA of FIGURE 1;

FIGURES 4 and 5 are elevation and plan views, respectively, of adifferent form of impeller from that shown in FIGURES l and 2;

FIGURE 6 is a plan view of another form of impeller;

FIGURES 7 and 8 are sectional elevation and plan views, respectively, ofyet another form of impeller; and

FIGURES 9 and 10 are sectional elevation and plan views, respectively,of a further form of impeller.

The pump shown in FIGURES 1 to 3, inclusive, comprises an impeller 12secured to the lower end of an impeller shaft 13 extending through anopening in the top wall 14 of a mixing vessel 25, and supported outsidethe vessel by a support frame 15. The shaft is coupled to an electricmotor 16, also mounted on frame 15, by a a linkage 17 which converts thecontinuous rotary motion of the output shaft of motor 16 intooscillating motion of the impeller shaft (and thus of the impeller),about the axis of the impeller shaft.

The impeller 12 comprises six radial vanes 20 secured to the impellershaft 13. This impeller is open ended and the pattern of flow throughthe impeller is indicated by the dotted lines designated 'F. The greaterpart of the flow from the impeller is in a radially outward horizontaldirection, although some flow, nearthe upper and lower ends is radiallyupwardly, and downwardly, respectively.

In the impeller shown in FIGURES 4 and 5, the radial vanes 243A arecapped b a shroud plate 21, which confines the flow near the upper endof the impeller to a substantially horizontal direction. The mass flowthrough this impeller is approximately half that obtained with theimpeller shown in FIGURES l and 2, but continuous flow is neverthelessachieved. The flow pattern is substantially the same as that produced byone half, say the lower half, of the open ended impeller.

The impeller shown in FIGURE 6 also has six vanes 20B, but these vanesare arranged in diametrically opposed groups of three. This impellerproduces aflow which is similar in the elevational view to that shown inFIGURE 1, but in the plan View the flow, as shown, is radially outwardsin diametrically opposite directions. If desired this impeller can beprovided with an end shroud 21A serving a similar purpose to the shroudplate 21 shown in FIGURES 4 and 5.

FIGURES 7 and 8 illustrate another form of impeller in which the vanes26C are surrounded by a cylindrical shroud 22. attached to the outeredges of the vanes. This shroud confines the flow to directionssubstantially parallel with the axis of the impeller.

A modified version of the last described impeller is shown in FIGURES 9and 10, and comprises, in addition to a cylindrical shroud 22A, anannular shroud 23. In this case the material flows through the centralopening in the end shroud 23 towards the lower end of the impeller andleaves the impeller in a' direction generally parallel to the impelleraxis.

In each of the open ended impellers illustrated in the FIGURES 1, 2 and6 to 10 inclusive, there are six vanes whose axial length is equal tothe impeller diameter, that is, dimension B (FIGURE 1) is equal todimension A (FIGURE 2). i

The impeller shown in FIGURES 5 and 6 has six vanes whose axial lengthis equal to half the impeller diameter.

The actual form of impeller for a given application will in generaldepend on the general pattern of flow required (having regard to theshape of the mixing vessel), and the attitude and position of theimpeller within the vessel. For example, if a generally horizontal flowis required with the impeller shaft vertical, one of the impellers shownin FIGURES 1, 4 and 5 or 6 would be chosen. But if a horizontal flow wasrequired with the impeller shaft horizontal, an impeller producing axialflow, such as those shown in FIGURES 7, 8 and 9, 10 would be used.

Each of the impellers illustrated can conveniently be manufactured intwo halves of welded or cast construction clamped together on theimpeller shaft.

Referring once more to FIGURES l and 3, the above mentioned supportframe comprises a support tube 30 secured at its foot to a base plate 31which in turn is detachably mounted on the top wall 14 of the mixingvessel. The impeller shaft 13 extends upwardly through the tube 30 andat its upper end is supported in a pair of silentblock bearings 32, 33mounted in a bearing block 34 fixed to the upper end of the supporttube. These silentblock bearings each consist of inner and outerconcentric bushes with a body of soft plastic material filling theannular clearance between them. The plastic material is bonded to bothbushes and seals the said clearance while permitting relative angularmovement between the bushes.

The impeller shaft 13 is formed with a collar 36 to whose cylindricalsurface a sealing tube 37 is clamped by a clamping ring 38. The sealingtube, which of course completely surrounds the impeller shaft is alsoclamped, by a clamping ring 39, to the outer cylindrical surface of aflanged bush 40 whose flange is secured to base plate 31. This tube isflexible in torsion and thus permits oscillation of the impeller shaftwhilst forming a fluid tight seal between the shaft and the opening inthe top wall of the mixing vessel. The sealing tube may be plain or maytake the form of a bellows whose corrugations are at right angles to theimpeller shaft, or at a more acute angle, or in the form of a spiral.

Preferably, and as shown, the impeller shaft 13 is in two portions,upper and lower, which are clamped together by a split bush coupling 41which can be released to permit removal of the lower portion of theshaft, together with the impeller, from the upper portion.

The electric motor 16 is mounted on a platform 42 attached to the upperend of the bearing block 34, and the output shaft of the motor iscoupled to the impeller shaft by the above mentioned linkage 17, whichis best seen in FIGURE 3 comprising a pair of arms 43, 44 pivotallyconnected to form a knee joint 46. Arm 43 is secured to the impellershaft, in between the bearings 32, 33 and arm 44 is pivotally connectedto an eccentric 47 carried by the motor shaft.

From a consideration of FIGURE 3 it will be seen that as the motor shaftrotates continuously, the impeller shaft will be made to oscillate aboutits own axis.

As stated above the impeller is so constructed that continuous, flow canbe achieved with an amplitude of oscillation of as little as 5. Howeverit is preferred to use a larger angle than 5 so that a larger mass flowthrough the impeller is established. In practice an angle of 15 has beenfound satisfactory, since it produces a satisfactory mass flow withoutintroducing excessive mechanical problems. In the embodiment shown inFIGS. 1, 2 and 3 the impeller is oscillated through an angle of 15".This is achieved by making the shaft or both the shaft and the vanesflexible and oscillating the upper end of the shaft through an angle ofless than 15. This flexibility of the shaft and, if applicable, thevanes is so adjusted that the natural frequency of oscillation of thesystem, including the inertia of the liquid lying between the blades ofthe impeller, is close or equal to the resonant frequency, and in thisway an increase in the amplitude of the impeller is obtained. Such anincrease in amplitude can of course be obtained for other resultantamplitudes of oscillation of the impeller. For example, if the impelleris to be oscillated through its minimum angle of 5, the shaft isoscillated through an angle of less than 5.

The motor 1-6 experiences an oscillating reaction and is preferablymounted on bearings or resilient mounts to minimise vibration.

While the mixing pump has been described as being in an uprightposition, it will be understood that it can Operate just as well in anyother attitude. Thus, whereas the usual requirement is for the shaft toextend vertically through the top wall of a mixing vessel, the pump canequally well be used with its shaft passing into a mixing vessel througha vertical or inclined side wall.

In a modified form of pump, generally similar to that described, thesealing tube arrangement is replaced by a third silent block bearingwhose outer member is sealed in the opening in the top wall of thevessel and whose inner member is secured to the impeller shaft, say justabove the split bush coupling 41, so that the length of the impellershaft is somewhat reduced. For some applications of course it is notnecessary to seal the impeller shaft to a wall of the mixing vessel inany way.

I claim:

1. A liquid-mixing device comprising a vessel adapted to contain aliquid to be mixed in the vessel, a rotary shaft flexible in torsion,mounting means supporting said shaft in a position extending into thevessel, an impeller secured to one end of the shaft for immersion of theimpellet into liquid contained in said vessel, said impeller including aplurality of vanes radially extending from the axis of the shaft, andoscillating rotary drive means coupled to a part of said shaft spacedapart from said impeller for oscillating said part through an angle ofrotation and at a frequency substantially equal to the resonantfrequency of oscillation of the system comprising the impeller, theshaft and liquid lying between said vanes.

2. A device as claimed in claim 1 wherein said impeller comprises acylindrical shroud coaxial with the said shaft and surrounding the vanesfor closing the gaps between the outer edges of adjacent vanes.

3. A device as claimed in claim 1 wherein said impeller comprises aplate disposed transversely to said shaft and having a centrallydisposed opening surrounding the shaft and overlying the inner portionsof the radial edges of adjacent vanes at one end of the impeller, saidplate closing the gaps between the outer portions of the radial edges ofsaid vanes at one end of the impeller.

4. A device as claimed in claim 1 wherein said vanes are arranged indiametrically opposed groups such that the gap between two pairs ofadjacent impellers are greater than the gaps between the remainingpairs.

5. A liquid mixing device comprising a vessel adapted to contain aliquid to be mixed in the vessel; a shaft flexible in torsion; mountingmeans supporting the shaft in a position extending into the vessel; animpeller secured to the shaft and immersed in said liquid, said impellercomprising a plurality of vanes extending along the axis of the shaftand projecting outwardly therefrom, the ratio of the axial length ofsaid vanes to the diameter of the impeller being not less than 2/5, andthe product of the number of vanes and said ratio being not less than 5,with some of said liquid lying between said vanes; and oscillating drivemeans coupled to a part of said shaft spaced from said impeller foroscillating said part through an angle and at a frequency substantiallyequal to the resonant frequency of oscillation of the system comprisingthe impeller, the shaft and the liquid lying between said vanes; wherebyoperation of said drive means causes said impeller to oscillate througha greater angle than said first-mentioned angle, said greater anglehaving a minimum value of 5.

6. A liquid mixing device as claimed in claim 5 wherein a shroud plateis disposed transversely of the shaft closing rigid.

is at least as great as 1:1.

8. A device according to claim 5, whereinsaid part of 5 the shaft isflexible, the remaining part of the shaft being 9. A device according toclaim 5, wherein said vanes are flexible.

10. A device as claimed in claim 1 wherein a shroud plate transverse ofthe shaft closes oneend of the impeller vanes, the other end being open,the minimum ratio of the axial length of said vanes to the diameter ofthe impeller being 2/5 and the minimum product of the number of vanesand the ratio being 2.5.

References Cited by the Examiner UNITED STATES PATENTS Bolton 259-101Brown 259-434 Lundahl 259134 Thompson 259-134 Morehouse 68132 Wahl259-128 Wenger 259-10 1 Clark 259-134 Examiners.

1. A LIQUID-MIXING DEVICE COMPRISING A VESSEL ADAPTED TO CONTAIN ALIQUID TO BE MIXED IN THE VESSEL, A ROTARY SHAFT FLEXIBLE IN TORSION,MOUNTING MEANS SUPPORTING SAID SHAFT IN A POSITION EXTENDING INTO THEVESSEL, AN IMPELLER SECURED TO ONE END OF THE SHAFT FOR IMMERSION OF THEIMPELLER INTO LIQUID CONTAINED IN SAID VESSEL, SAID IMPELLER INCLUDING APLURALITY OF VANES RADIALLY EXTENDING FROM THE AXIS OF THE SHAFT, ANDOSCILLATING ROTARY DRIVE MEANS COUPLED TO A PART OF SAID SHAFT SPACEDAPART FROM SAID IMPELLER FOR OSCILLATING SAID PART THROUGH AN ANGLE OFROTATION AND AT A FREQUENCY SUBSTANTIALLY EQUAL TO THE RESONANT FRE-